<div class="extra">
  <div class="extra-header">
    <p>
      <b>header</b>
    </p>
    <t-hole name="header">default header</t-hole>
  </div>
  <div class="extra-content">
    <p>
      <b>content</b>
    </p>
    <t-hole></t-hole>
  </div>
  <div class="extra-footer">
    <p>
      <b>footer</b>
    </p>
    <t-hole name="footer">default footer</t-hole>
  </div>
</div>
